Have Frame::tree() return a reference

Source/core/loader/ProgressTracker.cpp

Index: Source/core/loader/ProgressTracker.cpp
diff --git a/Source/core/loader/ProgressTracker.cpp b/Source/core/loader/ProgressTracker.cpp
index 7824a9175991ba1b5b0d34d66d5bd0be968884fb..060fce886106b222f3450e477e32995f8f83cf64 100644
--- a/Source/core/loader/ProgressTracker.cpp
+++ b/Source/core/loader/ProgressTracker.cpp
@@ -104,7 +104,7 @@ void ProgressTracker::reset()
 
 void ProgressTracker::progressStarted(Frame* frame)
 {
-    LOG(Progress, "Progress started (%p) - frame %p(\"%s\"), value %f, tracked frames %d, originating frame %p", this, frame, frame->tree()->uniqueName().string().utf8().data(), m_progressValue, m_numProgressTrackedFrames, m_originatingProgressFrame.get());
+    LOG(Progress, "Progress started (%p) - frame %p(\"%s\"), value %f, tracked frames %d, originating frame %p", this, frame, frame->tree().uniqueName().string().utf8().data(), m_progressValue, m_numProgressTrackedFrames, m_originatingProgressFrame.get());
 
     if (m_numProgressTrackedFrames == 0 || m_originatingProgressFrame == frame) {
         reset();
@@ -119,7 +119,7 @@ void ProgressTracker::progressStarted(Frame* frame)
 
 void ProgressTracker::progressCompleted(Frame* frame)
 {
-    LOG(Progress, "Progress completed (%p) - frame %p(\"%s\"), value %f, tracked frames %d, originating frame %p", this, frame, frame->tree()->uniqueName().string().utf8().data(), m_progressValue, m_numProgressTrackedFrames, m_originatingProgressFrame.get());
+    LOG(Progress, "Progress completed (%p) - frame %p(\"%s\"), value %f, tracked frames %d, originating frame %p", this, frame, frame->tree().uniqueName().string().utf8().data(), m_progressValue, m_numProgressTrackedFrames, m_originatingProgressFrame.get());
 
     if (m_numProgressTrackedFrames <= 0)
         return;